P0459

Evaporative Emission System Purge Control Valve Circuit High

P0459 is a generic OBD-II powertrain diagnostic trouble code: Evaporative Emission System Purge Control Valve Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0459
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P0459 means

P0459 — Evaporative Emission System Purge Control Valve Circuit High — is set when the PCM detects a voltage on the EVAP purge control solenoid (CPS) control circuit that is above the maximum valid threshold. It is the electrical complement and directional companion to P0458 (circuit low), and both sit within the broader purge valve fault family with P0443 (generic) and P0444 (open circuit).

A circuit-high reading on the purge valve control wire typically means the wire is open (broken or disconnected), the solenoid coil has an internal open circuit, or the control wire has shorted to the battery supply voltage. When the PCM attempts to ground the control wire to activate the solenoid, an open circuit leaves the signal rail pulled high by the PCM's internal pull-up resistor, producing a voltage that exceeds the active-low threshold. The PCM recognises this as a circuit-high condition and sets P0459.

A failed-open circuit (open wire or open coil) means the purge valve cannot be commanded on — it remains closed, preventing canister purge from occurring. Stored fuel vapours cannot be cleared from the charcoal canister, which will eventually saturate and allow raw fuel vapour to pass into the atmosphere or through the vent valve, producing a strong fuel smell. The EVAP I/M monitor will not complete. Unlike P0458 (shorted valve possibly stuck open), P0459 is less likely to cause a rich idle condition because the purge path is interrupted rather than continuously open. The MIL illuminates; no limp mode is induced.

Common causes

Most-frequently reported root causes when P0459 is logged.

  • 1
    Open circuit in the PCM control wire to the purge solenoid — broken wire, pulled connector pin, or corroded terminal preventing circuit completion.
  • 2
    Purge control solenoid coil with internal open circuit (broken coil winding), commonly caused by thermal fatigue.
  • 3
    Disconnected or damaged electrical connector at the purge valve.
  • 4
    Control wire shorted to the battery voltage supply rail (B+), pulling the signal continuously high.
  • 5
    Chafed or cut harness where the control wire has been severed by a sharp bracket or heat damage.
  • 6
    PCM internal output driver failure — rare; only after ruling out all external circuit causes.

Symptoms drivers notice

Malfunction Indicator Lamp (MIL / Check Engine Light) illuminated.
EVAP I/M readiness monitor does not complete — vehicle fails emissions inspection.
Fuel vapour smell near the fuel tank or charcoal canister as the canister saturates with uncleared hydrocarbons.
No rough idle or rich condition (purge valve remains closed, so no unmetered vapour enters the intake).
Possible mild increase in fuel vapour emissions over extended operation with no purge.
Scan tool may show EVAP purge solenoid commanded ON but actual circuit voltage remains high.

How to diagnose P0459

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze-frame data; note any companion EVAP codes (P0443, P0444, P0440).
  2. 2
    Locate and visually inspect the purge control valve connector and wiring harness for disconnection, corrosion, or heat damage.
  3. 3
    Disconnect the purge valve connector and measure coil resistance across the solenoid terminals; an open reading (infinite / OL) confirms an internally open coil — replace the valve.
  4. 4
    With the valve disconnected and KOEO, check for battery voltage (12 V) on the supply wire and continuity on the PCM control wire to the PCM harness connector; an open control wire confirms a wiring break.
  5. 5
    If the control wire shows 12 V when it should be close to 0 V (PCM ground), suspect a short-to-battery in the harness — inspect for insulation damage near power rails or ignition circuits.
  6. 6
    Use a bidirectional scan tool to command the purge valve; monitor the control wire with a multimeter — the PCM should pull it low (near 0 V) when commanded ON. If voltage stays high with a known-good replacement valve, suspect a PCM driver fault.
  7. 7
    After repair, clear DTCs and run the EVAP drive cycle to confirm readiness monitor completes.

Related powertrain codes

Frequently asked questions

Why does an open wire cause a "circuit high" reading instead of zero volts?

The PCM output driver circuit typically has an internal pull-up resistor connected to the reference voltage rail. When the PCM attempts to pull the wire low to activate the solenoid, if the wire is broken (open), no current flows through the solenoid coil and the pull-up holds the signal line at a high voltage. The PCM detects this high voltage when it expected low, and sets P0459.

How is P0459 different from P0458 in terms of driveability?

P0458 (circuit low / short to ground) may force the purge valve open continuously, causing a rich idle condition and potential fuel trim saturation. P0459 (circuit high / open) means the purge valve stays closed and no purge occurs — there is no rich condition, but the charcoal canister cannot be emptied, leading to saturation and fuel vapour smell over time. P0458 can have more immediate driveability impact; P0459 is typically a quieter fault.

Will the canister get damaged if I drive with P0459 for a long time?

The charcoal canister itself is relatively durable, but if the purge path is permanently closed and the vent valve is also restricted, pressure can build inside the EVAP system. More practically, a saturated canister may allow liquid fuel to migrate into the canister bed, degrading its adsorption capacity and eventually requiring canister replacement. Prompt repair avoids this secondary damage.

Disabling P0459 in software

RaceTune can permanently disable P0459 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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